The technology of coating substrates is well-developed, and methods for forming different combinations of coatings and substrates are described in the prior art. For example, processes for making printed circuits typically include steps of coating a substrate with one or more layers of material. However, new combinations of coatings and substrates typically present new problems which are not solved by methods available in the prior art.
It has been a goal to provide smooth, durable coatings of uranium oxide on various substrates so that the uranium oxide may be used as a source of fission fragments resulting from nuclear reactions. Fragments such as those produced by fissioning U-235 have been found to be useful as a source of energy for exciting laser systems. For example, see U.S. Pat. No. 3,952,263 entitled "Fission Fragment Excited Laser System" issued to MacArthur et al., which describes a system for exciting a laser including a source of neutrons for interacting with fissionable material to form fission fragments.
In order to minimize the absorption of fission fragments within a coating of uranium oxide, it is necessary that the coating be thin, i.e., preferably no more than about 5 microns thick. Adherent coatings of uranium oxide approximately 21/2 microns thick have been obtained by repetitive (10-15) brush or spray applications of a uranyl nitrate solution on a substrate, each coating step being followed by pyrolysis at a temperature greater than about 1000.degree. C. In carrying out this process it has been necessary to pyrolize the coating after each application of uranyl nitrate in order to reduce flaking and peeling of the uranium oxide such as would occur if a single thick layer of uranyl nitrate were pyrolized. This process has drawbacks in that the uniformity of coating is dependent upon the skills of the person spraying or painting, and the repititive process results in coating particles being shed throughout the sequence, resulting in radioactive contamination which requires expensive decontamination procedures.